假设 a = 2,b 值为 NULL,下表显示了 函数的返回值。
条件 | 条件判断结果 | LNNVL 返回值 |
a = 1 | FALSE | TRUE |
a = 2 | TRUE | FALSE |
a IS NULL | FALSE | TRUE |
b = 1 | UNKNOWN | TRUE |
b IS NULL | TRUE | FALSE |
a = b | UNKNOWN | TRUE |
假设有一张表 EMPLOYEES,给员工姓名列 name 和佣金列 commission_pct 里面插入数据,执行以下语句:
CREATE TABLE EMPLOYEES (name VARCHAR(20), commission_pct numeric);
INSERT INTO EMPLOYEEs VALUES ('Baer', null);
INSERT INTO EMPLOYEEs VALUES ('Bada', null);
INSERT INTO EMPLOYEEs VALUES ('Bates', 0.15);
INSERT INTO EMPLOYEEs VALUES ('Eros', null);
INSERT INTO EMPLOYEEs VALUES ('Girl', 0.25);
查询结果如下:
| COUNT(*) |
+------------+
+------------+
查询结果如下:
+------------+
| COUNT(*) |
+------------+
| 4 |